Marking of graphical elements is used to label these elements, bearing them with information that can be used for a variety of tasks like track and trace, security, inventory, expiration date controlling, chemical composition, place of manufacturing, etc. The modifications of the graphical elements are preferably done at a scale much smaller than the graphical elements' size and are thus preferably not perceptible to a human eye. Accessing the information stored in the marked graphical elements is achieved by taking images of these graphical elements with a camera and processing the images, for example electronically, in order to determine the nature and/or the amplitude of the marking that was done, i.e. the nature and/or the amplitude of the differences between the marked graphical element and the original one.
Graphical elements including brand names, graphical decorations, text, etc. are present for example on commercial products and/or on their packages. The application of a graphical element on a product or a package usually starts with a step of digital designing in which the graphical element is encoded as a digital file, for example a vector format or an image file, followed by steps of preprocessing, rasterization and printing, or application by any other suited method, of the graphical element on a surface.
The marking of the graphical element can be done at any of the above steps, but preferably at the step of digital designing. The steps of a typical method 54 for applying a marked graphical element and of a typical method 55 for detecting the marking and retrieving the stored information are schematically illustrated in FIG. 12. In a step of modifying the graphical element 50, the original digital file 49 representing the graphical element, for example a vector format file, is modified with the help of an editing software, in order to store information in the thus marked graphical element. This step of modifying the graphical element 50 is usually followed by a step of preprocessing for printing 51 and then by a step of printing 53 for actually applying the graphical element on a physical support such as for example a product and/or its package.
Once the product or package is produced, the graphical element on its surface contains the marking, and thus some piece of information, that can be read during a verification and/or decoding process 55. This process includes the steps of taking an image 56 of the graphical element, analyzing the image 57 and extracting the information stored in the marked graphical element 58.
Patent application US 2005/0039021 A1 describes a marking method, wherein marking is applied to text only and corresponds to changing spaces between words according to a specified grid. This method can thus not be applied for example to brand names consisting of a single word. Furthermore, this method does not allow a robust detection when the marked text is applied on a curved surface and/or when the text is distorted because of a stretching of its support, for example.
Patent application US 2009/0232352 A1 describes a marking method, wherein the graphical information is treated as an image and marking is performed on a global basis, which is not appropriate for preserving (?) smooth and clean edges of the marked (?) graphical elements.
An aim of the present invention is to provide a method for marking graphical elements, wherein the modification of the graphical elements is preferably invisible to human eye in order for example to not alter the brand's impact and/or to not be easily detectable, the presence of the marking being preferably only detectable with the help of appropriate image processing tools.
Another aim of the present invention is to provide a method for marking graphical elements and a corresponding method for detecting said marking that are robust to quality reduction or other possible deformations due to the printing process of the graphical elements and/or to later deteriorations of the surfaces bearing the graphical elements.
Another aim of the present invention is to provide a method for marking graphical elements and a corresponding method for detecting said marking that allow detecting the marking and recovering the information stored therein irrespectively of the curvature of the surface on which the graphical element is applied.
Still another aim of the present invention is to provide a method for marking graphical elements and a corresponding method for detecting said marking allowing for a simple and robust detection of the marking with camera-enabled mobile devices.